Can I use a 4s BMS on a 12v Battery Pack?

[Gorrillasnot]

Hello,

As a hobby I like to convert older NiCad tools to lithium..Mostly 12v stuff.
I ordered a bunch of BMS boards on aliexpress, but when they arrived I noticed I made a mistake and ordered 4s instead of the 3s I needed. It wouldn't be worth sending them back based on the turnaround time and cost to ship.
Can I use the 4s BMS boards in 12v packs? If so is there anything special I would need to do to make them work?
Probably a stupid question, but would it be better to ad a battery and run the 12v tools on 14.4v?

thanks

[Jwillis]

Depends on the board. On Some boards it is possible to add or subtract components to change the the number of series batteries. BUT, unless you know Exactly what components to add or subtract, including their values, things can go wrong very quickly. With that being said it is Advisable to get the boards that you require instead of modifying the ones you have. Use a 3s board for 3 series batteries.

Also keep in mind that those boards  from China can be either passive or active balancing. Some don't have low voltage cutoff and are designed for use with a control board. Some don't have short circuit protection. So you have to be careful which ones you purchase because they may not be what you expect.

[Gorrillasnot]

https://www.aliexpress.us/item/2251832665700493.html?spm=a2g0o.order_list.order_list_main.122.404c18029qCRpP&gatewayAdapt=glo2usa
The ones from that link that say 4s 40a balanced are the ones I bought.
If it's not a good idea to modify them for 3s would it be ok to build 4s batteries to use on 12v tools? For the little bit of money saved I'm guessing not, but I have to ask...I'm still learning .

thanks

[thm_w]

Looks like you could bridge out the fourth cell and then disable the protection on that cell.
Schematic: https://circuitdigest.com/electronic-circuits/lithium-ion-battery-management-and-protection-module-bms-teardown-schematics-parts-list-and-working

But its a $1 board, not worth it, I would just order the 3S.

[johansen]

 i run 5 cell 20v lithium batteries on older 12 volt dewalt drills.

you don't actually need to worry about the over voltage, the issue is the internal resistance of the nicd cells is what protects the motor from overcurrent.

almost all 12v nicd hardware will run fine on 4 cells lithium.

[pienari]

I used for years Bosch 12v units 14.4v and sometimes when 14.4v battery was charging 18v battery.
No any issues there.
Milwaukee 14.4v worked fine 18v li-ion battery.

[inse]

Same here, made 3s and 4s replacement for 12V NiCd powered Bosch drills.
No issue, just don’t overload the motors with the torque gain.